Belt drive modification

Ah, less technical lines you say?

CB250N you say?

Remember it well.

Gut reaction says kallifudging a set of pulleys from a gpz305 would be your first port of call.

Belt drive pulleys will need to be affixed to shaft quite firm so you'll have to clamp the pulley secure on the gearbox shaft, unlike the oe sloppy fit sprocket.

Then again I notice you have a photo of a belt and pulley. Are you trying to get that to fit? The one you have is not HTD style but that's ok as long it's up to the job. That can be checked out if I know whose make of belt it is.

Very funny,

My 1984 Honda 250 Rebel has a belt final drive. I like it a lot. Don't have to lube it.

Why not go out and look for an old 1984 Honda Rebel and save yourself a lot of trouble. They are probably pretty cheap.

JAG

Or just run a chain and lather it in wax.

Look on the bright side. The entire rear, left side of the bike won't go rusty.

Or the rear tyre.

Or your left side legging.

Or anyone tail gate ing you.

Hee Hee

Apart from bulky sprockets, which sounds very uncomfortable, the big problem with belts is they're very intolerant of varying sprocket centre distance changes. I don't know how the GPz305 coped with this, but the geometry has to be very carefully calculated to ensure with a suitable jockey wheel that the belt isn't stretched or relaxed as the suspension moves. Chains don't mind anywhere near as much.

Buell (remember them?) had a problem with belt breakages on the Lighting a few years ago (and with lots of other breakages too...) which a BMW engineer who'd worked on the F800 pointed out: Buell stored oil in the swingarm which meant it got very hot and expanded as the engine warmed,. I did a quick calculation and worked out it grew by around a millimetre, slightly more I think, when the oil was up to full temperature, and this was enough to over-tension the belt and snap it. Oops.

SilverCub - now you and I know that we share a similar fascination for a bike engineering challenge and a love of the more "off the beaten path". In this case however even I wonder what on earth you are up to and why? Just keep your Soup Dragon and slam a Scottoiler on there. Almost zero maintenance required and all the benefits of the now free thought time to think up off the wall mods for our Monkeys.

I'm not a real monkey!

Actually, it's an ape. If I were an ape I'd probably be offended. If... You.... See... Wha... Oh forget it.

If anyone has a spare "monkey" I'm game for a laugh. Long as me back will stand it. And me knees.....

Irony is that a belt can absorb changes in tension with some elasticity and that might help with transmission slap - somebody at Harley Davidson forgot that - with the XR 1200 which has a nice clean belt drive without the Buell Tensioner but has the gear slap of ironically a tractor -

as a feature though i love it - keep the bike clean !!

Sir Sid. Toothed belts will run better without a jockey pulley. Wherever a jockey pulley is there, it's always there as a get me out of jail card. When there's no other way around the tensioning requirement.

Toothed belts need a fair bit of tension to work best and are not as forgiving as you'd think. On a bike rear drive I'd say the roller chain will absorb more sudden torque fluctuations because it is relatively "floppy". Slack, if you will.

Jag. It never gets ABOVE 17 degrees where I live! I'd never be out. Don't go out much come November these days mainly because of the salt. Also because my pinkeys won't take it any more. As Kevin is finding out. (sorry, but it'll only get worse mate!). Back when I were a lad, used to ride all year round. I had an xl125 as a winter bike for a while. Used to go out just for a play in the snow. Brilliant.

1) Not usually, but if it isn't raining on the way out it will be on the way back.

2) You missed the key addition, no, not a belt drive, a 3rd wheel, helps a lot in the snow.

3) Yes, admittedly true. But this is solved with the aid of a roller brush and some military paint once the original finish has fallen off. The Guzzi in the pic took 4 winters of abuse before this happened though.

It's pretty much LOL all the way riding one too. When it's not AAAARRRHHH!!! that is.

Your dad was obviously a sensible chap.

Nowadays, I guess with the introduction of better belts, constant tension is not such a requirement. Many belt drive bikes now do not have fancy pulleys to keep constant tension and seem to work well enough.

There's a German company that offers a belt drive conversion for various machines, the Yamaha MT-01 being one and there's no additional tensioning mechanism other than there was for the chain.

The biggest problem with making a kit is finding a belt of the correct length. If it's not already made for another bike, then you're wasting your time. You can't simply add or remove links:-)

I love the idea of a lube free drive mechanism, but there are downsides. A belt can be noisy. They're more expensive than a chain and can be destroyed by a sharp stone getting caught up in the pulleys. They are also less elastic than a chain and can cause snatchiness. I'd certainly like to try one on a bike though.

Since they appear to be usable with much less tension, it shouldn't affect any bearings.

A problem with jockey wheels is also arranging that they keep the tension as desired. It would be quite complex to design a jockey wheel system to maintain absolutely constant tension. But it seems to be less of an issue now.